Interstice: What is it? Composition, Functions, Lymphatic System and Associated Diseases

The fluid in the connective tissue spaces is called interstitial fluid.

Interstitial fluid is essential because it bathes cells, supplies them with vital substances, and removes harmful ones.

A space that contains the fluid is known as an interstitial space or interstitium.

These fluid-filled spaces were discovered in connective tissues throughout the body, even below the skin’s surface, the lining of the digestive tract, lungs, urinary systems, and surrounding muscles.

The fluid in the body is classified according to its location. The extracellular and interstitial fluid are sometimes confused. Technically, interstitial fluid is a type of extracellular fluid.

Intracellular fluid is found within cells. Cells contain structures as well as fluids.

The extracellular fluid is outside the cells. It is generally said to include:


  • Plasma within the blood vessels.
  • Lymph within the lymphatic vessels.
  • Transcellular fluids (cerebrospinal fluid in the brain and spinal cord, synovial fluid in the joints, pleural fluid in the lungs, digestive and urinary tracts, etc.).
  • The interstitial fluid that bathes cells.

Transcellular fluids are surrounded on both sides by a layer of epithelium (a thin tissue that lines the channels and compartments of the body).

The interstitial fluid leaves the bloodstream and bathes the cells.

It is also known as tissue fluid. Excess tissue fluid drains into the lymphatic vessels.

The tissue space, interstitial space, or interstitium is located between the blood and lymphatic vessels and cells. It contains both interstitial fluid and molecules that make up the extracellular matrix or ECM.

The ECM provides mechanical, adhesive, and biochemical support for cells.

Blood vessels

The interstitial fluid comes from the plasma in the capillaries. Blood contains red blood cells, white blood cells, platelets, and liquid plasma. Leave the heart in the aorta. This vessel then branches into multiple arteries.

The arteries divide into narrower arterioles and split into tiny capillaries within the tissues. Some veins are so thin that red blood cells must pass through them in a single row.

Some of the plasma leaves the capillaries and enters the spaces around the cells, forming an interstitial fluid.

The fluid contains materials that cells need, such as nutrients. Cells absorb nutrients and also release waste into the interstitial fluid.

Hydrostatic and osmotic pressure

Two forces control the direction of fluid movement between the capillary and the tissue spaces. One of them is hydrostatic pressure, and the other is osmotic pressure.

Hydrostatic pressure

In biology, hydrostatic pressure is sometimes defined as the pressure of a fluid in a closed space. In capillaries, the closed area is inside a vein.

Blood pressure created by your heartbeat determines hydrostatic pressure.

Hydrostatic pressure is highest at the end of a capillary closest to the heart’s pumping chamber and lower at the other end.

Concentration gradient

The membranes surrounding and within cells are semi-permeable. They allow some substances to move through them but block others.

Substances move through a semi-permeable membrane according to their concentration gradient, that is, from a region where they are more concentrated to one where they are less focused.

Water molecules follow this rule.

The movement of water through the membranes is so crucial that particular terminology is used to describe it.

Osmotic pressure

Osmotic pressure can be defined as the ability of a solution to absorb water through a semi-permeable membrane.

Like other substances, water molecules move from where they are most concentrated to where they are least complete.

A solution with a low concentration of water molecules has a great attraction for water and is said to have high osmotic pressure.

Capillary tissue fluid exchange

In capillaries, hydrostatic and osmotic pressure can partially or entirely cancel each other out.

The higher pressure wins the “competition” by controlling the direction of movement of the water through the capillary wall.

The hydrostatic pressure decreases during the travel of the blood through the capillaries, while the osmotic pressure remains the same.

At the end of the capillary closest to the artery, the hydrostatic pressure in the blood is higher than the osmotic pressure of the blood.

The higher hydrostatic pressure “wins” the competition, so the fluid predominantly moves out of the capillary.

Hydrostatic pressure pushes water and dissolved chemicals into the bloodstream and tissue spaces. In this way, the interstitial fluid is formed. The process is known as filtration.

The hydrostatic and osmotic pressures are equal in the middle of the capillary. Neither predominates in the movement of water outward or into the vein. However, a net activity of substances still occurs due to another factor.

Substances move through the capillary wall according to their concentration gradients. This happens everywhere in the capillary but is often clouded by pressure forces.

At the venular end of the capillary, the hydrostatic pressure in the blood is lower than the osmotic pressure of the blood. Now osmotic pressure wins the competition.

The fluid predominantly exits the interstitial space and enters the capillary. This process is known as reabsorption.

The lymphatic system

The amount of fluid that leaves the capillaries and enters the tissue spaces is greater than the amount that returns to the veins.

The lymphatic system picks up the excess fluid in the interstitium. This system consists of branching vessels, like the circulatory system. However, the ship contains lymph instead of blood.

Also, the lymphatic system is a one-way system. Small blind end lymphatic vessels are found in tissue spaces. These lead to wider glasses.

Over time, the lymph drains into a blood vessel.

The walls of the lymphatic vessels are permeable to liquids and dissolved substances. Lymph is quite similar in composition to blood plasma.

Unlike blood, it does not contain red blood cells or platelets, but it does have white blood cells.

Transporting fluid through the lymphatic vessels before returning to the blood vessels offers advantages. Lymph nodes are enlarged areas in the lymphatic vessels.

They kill pathogens (disease-causing microbes), cancer cells, and other harmful particles. They are an essential part of the immune system.

Composition and functions of interstitial fluid

Interstitial fluid is a water solution that contains solutes (dissolved substances). Capillaries are often said to supply nutrients to cells and remove waste.

However, interstitial fluid plays a more direct role in this process, as it forms a liquid connection between capillaries and cells. The main components of interstitial fluid include the following substances:

  • Sugars: simple carbohydrates, like glucose.
  • Salts: ions and ionic compounds.
  • Amino acids: the building blocks of proteins.
  • Fatty acids: essential building blocks of fats.
  • Coenzymes – Molecules that help enzymes do their job
  • Signaling molecules:  that pass messages from one cell to another.

Interstitial fluid gives cells the chemicals they need to survive, including nutrients and oxygen. It also carries signaling molecules between cells.

As their name suggests, signaling molecules carry signals to other cells, triggering specific behaviors.

Waste, including carbon dioxide and urea, is carried out of cells by interstitial fluid.

Dense connective tissue

An intriguing study may have discovered more about the interstitium, as it exists in dense connective tissue. A group of researchers surveyed various US institutions.

The dense connective tissue provides strength where it is needed in the body. The tissue contains fibers of a protein called collagen. In the traditional view of weaving, these fibers are arranged in a compact arrangement.

Tissue is found in many places in the body, including the lining of the digestive tract, urinary tract, and lungs, around blood vessels, under the skin, in tendons and ligaments, and around muscles.

Based on their new observations, the researchers say that dense connective tissue contains interstitial spaces, as well as collagen fibers.

They say that the traditional method of examining pieces of body tissue collapses the fluid spaces in the tissue and causes fluid loss.

The tissue undergoes a unique process before it is examined under a microscope.

It is subject to many stresses, including the addition of a preservative, dehydration, and staining.

These steps often produce a beautiful sample to observe, but the image may not be a completely accurate view of living tissue.

Interstitial lung disease

Interstitial lung disease (also called diffuse parenchymal disease) is used to describe several different disorders that affect the interstitial space.

The interstitial space consists of the walls of the lungs’ air sacs (alveoli) and the areas around the blood vessels and small airways.

Interstitial lung diseases result in an abnormal accumulation of inflammatory cells in the lung tissue, cause shortness of breath and cough, and have similarities in an appearance on imaging studies but are not related in any other way.

Some of these diseases are very rare.

Early in these diseases, white blood cells, macrophages, and protein-rich fluid accumulate in the interstitial space, causing inflammation.

If inflammation persists, scarring (fibrosis) can replace normal lung tissue.

As the alveoli are progressively destroyed, thick-walled cysts (called honeycombs because they look like cells in a hive) are left in place.

The condition that results from these changes is called pulmonary fibrosis.

Although the various interstitial lung diseases are separate and have different causes, they have similar characteristics.

All of these lead to a decreased ability to transfer oxygen to the blood, all of which causes stiffness and shrinkage of the lungs, making it difficult to breathe and causing coughing.

However, removing carbon dioxide from the blood is generally not a problem.


The most common symptoms of PID are shortness of breath with exercise and a non-productive cough. These symptoms are generally slowly progressive, although rapid worsening can also occur.

Some people may also have a variety of other symptoms. They may include fever, weight loss, fatigue, muscle and joint pain, and abnormal chest sounds, depending on the cause.

  • Chest x-ray and computed tomography.
  • Pulmonary function tests.
  • Arterial blood gas analysis.

Because interstitial lung diseases cause symptoms similar to more common disorders (e.g., pneumonia, chronic obstructive pulmonary disease), they may not be initially suspected.

When interstitial lung disease is suspected, diagnostic tests are done. The tests can vary depending on the supposed condition, but they tend to be similar.

Most people have a chest x-ray, chest computed tomography (CT) scan, lung function tests, and arterial blood gas tests.

CT is more sensitive than a chest x-ray and helps doctors make a more specific diagnosis. CT is performed using techniques that maximize resolution (high-resolution CT).

Pulmonary function tests often show that the volume of air the lungs can hold is abnormally small.

Arterial blood gas tests measure the levels of oxygen and carbon dioxide in the arterial blood and determine the acidity (pH) of the blood.

To confirm the diagnosis, doctors sometimes remove a small sample of lung tissue for microscopic examination (lung biopsy) using fiberoptic bronchoscopy.

A lung biopsy done this way is called a transbronchial lung biopsy.

A larger tissue sample is often needed and must be removed surgically, sometimes with the use of a thoracoscope (a procedure called a video-assisted thoracoscopic lung biopsy).

Blood tests can be done. They usually cannot confirm the diagnosis but are done as part of the search for other similar disorders.

The cause of interstitial lung disease is not known. The main factors influencing tobacco use are inhalation of environmental or occupational pollutants, such as organic and inorganic dust.

Other factors that should include: Certain drugs or medications, Certain connective tissue or collagen diseases, and sarcoidosis. Family history.


Because there are so many causes, treatment can vary. Some interstitial lung diseases have no cure.

Treatment aims to prevent more lung scarring, manage symptoms, and help you stay active and healthy.

Treatment cannot repair lung scars that have already occurred.

Treatments can include:

  • Lung transplant.
  • Oral (oral) medications, including corticosteroids to reduce inflammation and cyclophosphamide, suppress the immune system.
  • Pulmonary rehabilitation.
  • Getting a flu shot each year can help prevent flu and pneumonia.

Also, pneumococcal bacteria can cause minor problems, such as ear infections.

But they can also develop into diseases of the lungs (pneumonia), the life of the brain, spinal cord (meningitis), and blood (bacteremia).

However, anyone can get the pneumococcal disease, children over 65, people with health problems, and smokers.

Talk to your healthcare provider and your child’s provider about the pneumococcal vaccine.